linux-kernel - Re: [PATCH] ALSA: hda: Use maple tree register cache

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Date:   Tue, 13 Jun 2023 16:49:41 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ALSA: hda: Use maple tree register cache

On Tue, Jun 13, 2023 at 04:24:28PM +0200, Takashi Iwai wrote:
> Mark Brown wrote:

> > BTW I was just looking at reg_raw_update_once() and I can't figure out
> > why it's trying to do what it's doing - it does a read to check if it's
> > seen the register before and then does an _update_bits() if the register
> > hasn't been cached yet, apparently trying suppress duplicate writes but
> > possibly deliberately discarding changes to multiple bitfields in the
> > same register.  That's not what the non-regmap path does, it'll only
> > discard noop changes to the same bitfield.

> Yes, it's a quite hackish way of optimization of the initialization.

> Since HD-audio codec has no known default values unlike normal codecs,
> it needs to initialize itself only at the first access, and this
> helper does it.

Ah, if it's just suppressing the write the code should just be removed.
regmap_update_bits() already suppresses noop writes so unless we might
write a different value to the register later the effect will be the
same.  I can send a patch.

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